Re: [PATCH/RFC 0/4] Probe deferral for IOMMU DT integration

From: Laura Abbott
Date: Mon Feb 09 2015 - 16:38:41 EST

On 2/7/2015 2:41 PM, arnd@xxxxxxxx wrote:
Laura Abbott <lauraa@xxxxxxxxxxxxxx> hat am 6. Februar 2015 um 01:31

The requirement for this is based on a previous patch to add clock
support to the ARM SMMU driver[2]. Once we have clock support, it's
possible that the driver itself may need to be defered which breaks
a bunch of assumptions about how SMMU probing is supposed to work.

Hi Laura,

I was hoping that we would not need this, and instead treat the iommu in
the same way as timers and SMP initialization, both
of which need to be run early at boot time but may rely on clock controllers
to be initialized first.

Is there a specific requirement that makes this impossible here, or is your
intention to solve the problem more nicely by allowing deferred probing
over forcing the input clocks of the iommu to be early?


The current clock driver for qcom targets doesn't support the early
initialization needed for timers and SMP because neither of those depend
on the clocksources. I discussed this with Stephen some and adding the
early support would not mesh well with the device/driver design of the
current clock driver so that's not really an option right now.

I do think the deferred probing design is cleaner. Even cleaner would
be a proper bus type but that's a different can of worms.


Qualcomm Innovation Center, Inc.
Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum,
a Linux Foundation Collaborative Project
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at
Please read the FAQ at